In many turbine and boiler installations fuel combustion occurs at the outlet of a burner which is encircled by a register. Typically, the burner is mounted at an aperture in a furnace wall and injects fuel through that aperture. The register provides a path for supplying external air to the injected fuel. Air is induced to flow through the register to the burning fuel by either a forced air duct or by a natural chimney draft. The register operates to adjust the volume flow of air in order to establish an air to fuel ratio consistent with high efficiency and complete combustion. For a system having several burners which are supplied by common air ducts it is also important to regulate the airflow to maintain a balance among the burners.
A widely used register employs rotatable vanes which act like louvers. In this arrangement the volume flow of air depends upon the extent to which the vanes are aligned with or tranverse to the flow of air toward the burner. In addition to regulating the volume of airflow, these vanes uniformly surround the burning fuel with an inward airflow which fosters a homogenous mixing of air and fuel. While this register operates satisfactorily it employs many moving parts and associated linkage.
Since a register is a structure which is open in the sense that air must pass through it, a balance between structural rigidity and the free passage of air is a significant consideration. To provide rigidity and proper mixing of air and fuel a register described herein has vanes which are affixed between two annular members. The volume of airflow is regulated by a movable sleeve which travels on guides disposed around the vanes so that the vanes are enshrouded a variable amount. With the sleeve adjusting air flow, the vanes provide structural strength and rigidity. In addition, since relatively few moving parts are required, reliability is enhanced.